This invention relates to a handling device for a power working machine and, more particularly, to a lever mechanism of a handling device which is rotatably attached to the rear portion of a portable power working machine such as a hedge trimmer.
A portable power working machine such as a hedge trimmer generally has a power source case enclosing a power source such as an internal combustion engine or an electric motor, a mount base portion enclosing a transmission case including a power transmission device such as gears to be actuated by the power source, a working portion comprising clipper blades to be actuated via the power transmission device by the power source, and a handling portion attached to the power source case or the mount base portion. For convenience of manipulation, the handling portion includes a front handle portion and a rear handle portion. The rear handle portion is provided with a throttle lever for adjusting the opening degree of a throttle valve in case of the internal combustion engine is to be employed as a power source.
Generally, the throttle lever is manipulated with an operator's finger, and the opening degree of the throttle valve is adjusted by rotationally manipulating the throttle lever via a throttle cable. In a typical carburetor design, the throttle valve is normally biased at a minimum opening degree (idling opening) for maintaining the throttle valve at the idling opening. When the throttle cable is pulled by a predetermined length or more, play is eliminated and the throttle valve moves from the idling opening to a high-speed rotation opening.
The throttle lever for controlling the opening degree of the throttle valve is of automatic-opening-return type, automatically to return the lever together with the throttle valve to the initial position (idling opening) whenever manipulation of the throttle valve is suspended. With such a throttle lever, the internal combustion engine automatically returns to idling when the operator's finger releases the throttle lever. Thus, if the working machine is designed with transmission of engine driving force to the working portion via a centrifugal clutch, the centrifugal clutch is brought into a cutoff condition upon releasing of the finger, so that power transmission to the working portion is interrupted and operation of the working portion is terminated. However, if it is desired to perform work with the throttle valve at an intermediate opening degree, the throttle lever must be maintained at a desired intermediate rotational position with the finger. As the finger fatigues, manipulation may become irregular.
As a remedy, a hand lever device for a portable power working machine has been proposed wherein a sub-lever is mounted, in addition to a main throttle lever, for pulling and adjusting a cable connected with the throttle valve by making use of a turn around member such as a movable pulley, and for making the turn around member movable by making use of a throttle lever (Japanese Patent Unexamined Publication H/8-303262). As the opening degree of the throttle valve can be adjusted, via a cable, by making use of the sub-lever in such a hand lever device for a portable power working machine, the opening degree of the throttle valve can be set to a desired degree even under conditions where the throttle lever is fully rotated, and still the throttle lever can be immediately returned to the minimum opening degree (idling opening).
However, the distance of pulling the cable connected with the throttle valve by means of the sub-lever in such a hand lever device for a portable power working machine is equivalent to the distance of rotating the sub-lever, so that it is impossible to adjust the opening degree throughout the entire opening degree range of the throttle valve unless the sub-lever is rotated to a relatively large extent. Therefore, in order to assure a required distance of rotation of the sub-lever, a relatively large rotation range is required, making it difficult to miniaturize the device. Furthermore, since the sub-lever is spaced away from the throttle lever as a main lever by a relatively large distance, it is difficult to adjust the sub-lever while holding the throttle lever with a finger, thus impairing operability.